The invention relates to a heat sink and to an assembly or module unit or arrangement.
It is generally a standard and necessary practice to cool electrical or electronic components or assemblies, in particular power components or assemblies or modules to dissipate heat loss, namely by means of at least one heat sink (cooler) comprising at least one cooling element. For this purpose, the existing art uses in particular heat sinks with cooling elements in which at least one, preferably highly branched cooling channel structure is provided, through which a liquid and/or gaseous and/or vaporous heat-transporting or medium or cooling medium, for example water, can flow.
For optimal cooling, it is advantageous in many cases to connect such components or assemblies by means of a solder bond to an outer cooling surface of the cooling element of the heat sink. The cooling element in this case, at least in the area of its outer cooling surface, is made of a metal material with high thermal conductivity, in particular, a copper or aluminum. The solder bond between the component or assembly and the cooling element features the advantage, for example, that both components can be manufactured separately and connected with each other after being manufactured.
Problematic, however, is the fact that the solder bond or solder layer between the respective cooling element and the part of the constructional or modular unit comprising the at least one electric component, due to the generally widely differing thermal expansion coefficients of the components connected with each other by the solder layer, is subjected to considerable mechanical stress caused by thermal factors. This is especially pronounced in case of frequent changes in temperature, such as in the case of a constant load variation in the electrical component or electrical assembly, as is the case with electric drive controls, for example. This thermally related mechanical stress causes premature aging of the solder bond and in extreme cases even partial or total separation of the solder bond and therefore loss of the required cooling of the component or assembly.
The “DCB process” (direct copper bond technology) is known in the art, for example for connecting metal layers or sheets (e.g. copper sheets or foils) with each other and/or with ceramic or ceramic layers, namely using metal or copper sheets or metal or copper foils, the surfaces of which are provided with a layer or coating (melt-on layer) resulting from a chemical bond between the metal and a reactive gas, preferably oxygen. In this method, which is described for example in U.S. Pat. No. 3,744,120 and in DE-PS 23 19 854, this layer or coating (hot-melt layer) forms a eutectic with a melting temperature below the melting temperature of the metal (e.g. copper), so that the layers can be bonded to each other by placing the foil on the ceramic and heating all layers, namely by melting the metal or copper essentially only in the area of the hot-melt layer or oxide layer.
This DCB method then comprises the following steps:                oxidation of a copper foil so as to produce an even copper oxide layer;        placing of the copper foil on the ceramic layer;        heating the composite to a process temperature between approx. 1025 and 1083° C., e.g. to approx. 1071° C.;        cooling to room temperature.        
Also known is the so-called active soldering method (DE 22 13 115; EP-A-153 618) for bonding metal layers or metal foils forming metallizations, in particular also of copper layers or copper foils, with ceramic material. In this process, which is used especially for manufacturing a metal-ceramic substrate, a bond is produced at a temperature of 800-1000° C. between a metal foil, for example copper foil, and a ceramic substrate, for example aluminum-nitride ceramic, using a hard solder, which in addition to a main component such as copper, silver and/or gold also contains an active metal. This active metal, which is at least one element of the group Hf, Ti, Zr, Nb, Ce, creates a bond between the solder and the ceramic through a chemical reaction, while the bond between the solder and the metal is a metallic hard solder bond.
It is an object of the invention is to present a heat sink that eliminates the above disadvantages.